Mobile radiotelephone method and system and terminal used in such a system

ABSTRACT

The method implements mobile terminals and an operating infrastructure having at least one call center, each portable terminal being given a credit of telephone charging units that is determined before said terminals are purchased, and each having means for calling a single call center. On the first occasion a call is made from a terminal, the terminal transmits an identifier to the single call center and the call center transmits a temporary subscriber number to the terminal, thereby enabling said terminal to be called via the network, and said number is stored in the call center.

BACKGROUND OF THE INVENTION

The invention relates to telephony by means of mobile terminals and anetwork operating infrastructure which is generally fixed but whichcould also include relaying via satellites in low orbit. A particularlyimportant, although non-exclusive application of the invention lies indigital telephony.

Existing systems for digital cellular telephony, such as GSM and DECT1800, comprise a network of base stations capable of communicating withone another and with mobile terminals, and the structure of such anetwork is complex for reasons of confidentiality, of international use,and of transmission security. Such systems require a potential user todeal with a limited number of points of sale and to take out asubscription that binds the user for a period of time that is generallylong and that comes to an end only on deliberate termination. Theseconstraints dissuade many people who need a mobile telephone only forvery short periods of time, during which it is unusual for them tooccupy locations that are very far apart from one another. The samedrawback exists for other cellular networks and remains even whenimplementing the UMTS standard.

The sale of smart cards for inserting into a standardized terminal andcontaining a fixed number of prepaid telephone charging units provides asolution that is effective in part only, since the user must still haveavailable a standard terminal that is complex. In addition, theintroduction of such cards has increased the number of thefts ofterminals.

Discardable cellular telephones are also known (WO-A-96/03001).

SUMMARY OF THE INVENTION

The invention seeks essentially to provide a method and a system formobile radio telephony that gives immediate access to the network onpurchase of a terminal, that is of low cost, and that allows telephonecalls to be made during a limited length of time only, while beingcomparable in convenience to a complex cellular telephone, and withoutrequiring a public telephone to be found.

To this end, the invention proposes in particular a radio telephonymethod implementing a network having at least one call center andportable terminals each given a predetermined credit of telephonecharging units and each having fixed means for calling a single center,in which method, on the first occasion a call is made from a terminal,the terminal transmits an identifier to the single call center and thecall center transmits a temporary subscriber number to the terminal,thereby enabling said terminal to be called via the network, and saidnumber is stored in the call center.

On each call from the terminal, the debit is incremented and is comparedwith the credit, or is debited from the credit. When credit has beenexhausted, calls from the terminal are rejected and/or the terminal isinvalidated, and its subscriber number is released, possibly after aperiod of time.

The invention also proposes a digital radio telephony system comprisinga network having at least one call center and having portable terminalseach of which stores identity data, a call number for a single centerbelonging to the network, and optionally an indication of an initialnumber of units that can be transmitted to the center.

Finally, the invention proposes a terminal that is usable in a system ofthe kind defined above, the terminal including a speech encoder/decoderconnected to means for transmitting/receiving a carrier that ismodulated by a speech signal, a preprogrammed memory that is notaccessible for writing and that is protected for reading, the memorycontaining an identifier, means for making a call to a single callcenter having a predefined number that is stored, and for transmittingthe identifier, optionally together with prerecorded credit,transmission being in secure form. It is nevertheless more convenientfor the credit to be deduced by the network from the identifier that itreceives. The identifier should comply with the standards of the radionetwork used, e.g. the 11 to 15 digit standard presently provided inGSM.

To reduce the cost of the terminal, it is possible to provide it with asingle call button causing a link to be established with the call centerby ‘dialling’ the number of the center, assuming that only outgoingcalls are authorized. Nevertheless, it is preferable to provide one ormore buttons enabling the terminal to be switched off, to be put onstandby (to receive calls), to answer an incoming call, and to seize aline to make an outgoing call.

The screen usually provided on cellphones can be omitted, thereby alsoreducing cost. However a monochrome or a color liquid crystal screen canbe maintained for the purpose of displaying prerecorded messages thatare stationary or animated, including advertising messages or games, soas to create a collectible. However the screen is not intended todisplay telephone information.

The invention has numerous applications since various circumstances makeit essential to have a mobile telephone even though a subscription isnot otherwise justified or when the conditions required for obtaining asubscription are not satisfied (e.g. people away from home).

By way of non-limiting example, mention can be made of children on anoccasional trip, in particular during school holidays, people having abad credit rating, and managers working away from the office undercircumstances where there is reason to fear that a conventional mobiletelephone will break down, be stolen, be lost, or be forgotten.

The terminals can be sold in supermarkets or in tobacconists, for aprepaid amount which may be accompanied by the constraint of telephoningonly from or only to the country of sale. To reduce the cost price ofthe terminal, its case may carry advertising with a contribution tocosts coming from the advertiser.

The telephone number allocated to the purchaser is kept valid so long asa credit balance remains and/or so long as a term of validity has notexpired, and it enables the purchaser to be called, including fromabroad, via the network with which the telephone is associated. Theterminal is generally not rechargeable so as to avoid risks of fraud.

The operating principle can implement means comparable to those used forphone cards and for GSM, but in highly simplified form, particularly inthe most common circumstance of no recharging being provided for.Nevertheless, and this is an essential difference, the prepaid amount isdebited by the network on the basis of the credit communicated by thecall center. Terminals are invalidated after their credit has been usedup and/or after their period of validity has expired, but they mayoptionally be collected so that various components thereof can be reusedseveral times over, e.g. the vocoder and the high frequency head (ashappens with so-called discardable cameras). Management at the callcenter and at the charging center is very simple and very flexible. Theinitial credit can be decremented progressively with the caller beinginformed of the balance by the call center each time a new call is made.Consumption can be determined as use takes place and compared with theinitial credit. The option of receiving calls can be maintained byprogramming at the call center for a determined duration after credithas expired, possibly accompanied by a message indicating that credithas expired.

The initial operations of putting into service by allocating a number,and then of establishing a call can be performed by means of a voiceserver. Nevertheless, it is not always justifiable, these days, to makeuse of human operators.

The identifier can be implemented in a manner comparable with that usedin GSM and can be calculated on the basis of a serial number, amanufacturer's number, etc. which numbers are inaccessible from theoutside and are calculated by means of an algorithm such as the dataencryption standard (DES), or the Rivest Shamir Adleman (RSA) algorithm,or an algorithm requiring zero knowledge input.

To simplify the terminal, it is preferable to avoid data transfer otherthan transfer of data required for initializing the terminal, forrecognizing it, and for locating it within the cellular network.

The system can use the infrastructure of an existing cellular radiotelephone network. This infrastructure generally includes fixed stationseach allocated to a particular cell, and base station controllers whichmanage all of the cells in a determined region. The way in which a linkis set up with the appropriate base station and at the initiative of aterminal of the invention can be the same as that used for conventionalterminals, except that the call number authorized for the terminal is asingle number and gives rise to routing to a single call center capableof accessing the general network. The call center includes access means,means for forwarding a call to the desired other party, and means forhandling payment. The functions to be performed can be summarized asfollows:

Distributed Telephone Management

Serial numbers or manufacturers' numbers of telephones (or some otheridentifier) are communicated to the call center either when thetelephones enter the sales network, or else when they are sold. If thisoccurs on sale, the consequences of a batch of telephones ready for usebeing stolen on leaving the factory are minimized.

Various checking means can be used to reduce fraud. One consists in thecall center recording the serial numbers or the manufacturers' numbersof all of the telephones that have been distributed (together with theprepaid amounts allocated thereto if they vary depending on the type ofappliance). Once a first call has been made from a terminal, the callcenter identifies the terminal by data interchange implementing anenciphering algorithm that makes it impossible to recognize the numberby eavesdropping the interchange. Subsequently, the balance can bechecked by using the same means to verify that the amount taken intoaccount and the amount which remains and which is indicated by theterminal are consistent, assuming that the terminal is capable ofoperating in this way.

Given that the sums of money involved remain small, simple algorithmswith zero knowledge input can be used. Nevertheless, it is also possibleto use more complex algorithms such as the DES or the RSA algorithms.

Handling Payment

Payments can be handled by an operator, which is the simplest solutionto implement, or automatically by speech recognition and speechsynthesis at the call center.

With an operator, when a call is set up, the operator can inform theproprietor of the terminal of the balance remaining. The operatorengages the charging mechanism. The network will interrupt the call ifthe balance drops to zero, possibly after giving an audible warning, andthe data relating to the terminal is deleted from the call center at theend of a predefined period of validity. At the end of a call, thebalance is updated and can also be recorded in the terminal. It istransmitted to the caller by voice. Additional consistency checks can beimplemented (consistency between the type of amount allocated and thedestination of the call, . . . ). Rules can be provided for auditing thefile. In particular, terminals can be sold with an indication of aperiod of validity beyond which the data relating to the terminal willbe deleted from the call center. To prevent an out-of-date terminalbeing used for call attempts that will fail but that will neverthelessmake use of resources in base stations, the terminal can be designed sothat the transmitter means of the high frequency head can be disabled byan order issued from the network.

Call Management

On the first call (e.g. identified by the fact that no call number hasyet been allocated to the identifier in a database), a number isallocated and is given to the purchaser by voice, and is memorized.Making calls from the center, when a request is received, is aconventional operation and is easily performed using human operators. Itis easy to exchange information by voice, thereby making it pointless toprovide the terminal with a display screen, thereby reducing cost, size,and power consumption.

It is also possible to use voice synthesis to inform the holder of theterminal and to use voice recognition to identify the number the holderwishes to call by spelling out the subscriber digits. Such a vocalserver system can use means comparable to those already put intooperation by France Télécom to provide information about what's on invarious regions.

Call handling is simple when the terminals are sold with informationthat they are good for national calls only, and in a given languageonly. Nevertheless, the user may be given the option of using a languageother than that of the country of sale, by implementing one or other ofvarious solutions, e.g.:

access to the call center of the country of sale followed by diversionto an operator speaking the selected language;

direct selection of language by the purchaser when the discardableterminal is initialized; a program resident in the terminal is thenprovided to enable the purchaser to select a language and to allocatethe access number for the center operating in the selected language tothe call button provided on the terminal.

When calls are processed automatically, a single center may includemeans for analyzing and synthesizing speech in several languages.

Handling centralized in just one call center per country gives theadvantage of centralizing all data in a single location in which creditis recorded and where debits are made.

In order to protect the environment, provision can be made to return adeposit and/or to reduce sale price in the event of a used appliancebeing handed in. Some of the components can be reused, with each usebeing indicated by a mention applied to the component so as to ensurethat each component is eventually discarded after being used a givennumber of times. Power can be provided by electrochemical primarybatteries or by solar cells. The use of rechargeable batteries is notjustified given the short working life and the lack of means forreloading credit units.

There follows a description by way of non-limiting example of onepossible structure for a mobile radio telephone terminal of theinvention. The description refers to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a terminal showing the components thatappear on its front face;

FIG. 2 shows one possible appearance of the bottom portion of the rearor front face, showing a battery level indicator;

FIG. 3 is a block diagram; and

FIG. 4 shows another possible disposition for the switch means.

DETAILED DESCRIPTION

The portable terminal shown in FIG. 1 comprises a case made of two partsthat are snap-fastened or welded together. The front face has windows 10for an earpiece and 12 for a microphone, together with a set of fourbuttons 14 designed so that only one of them can be depressed at a timeso as to impart a well-determined state to the terminal. In other words,each depressed position of one of the buttons excludes any of the otherbuttons taking up a depressed position. Light emitting diodes (LEDs) 15give essential information, e.g. the state of the terminal(transmit/receive or receive only). In FIG. 1, each button may includeits own LED, e.g. seen through the button which is transparent.

The rear face is provided with a flap enabling batteries to be installedand with a battery-receiving hatch. An LED placed in the back can showbattery level (FIG. 2). Insufficient battery voltage can be indicated bya change in color or by flashing or by a sound signal. A large area canbe left available for an advertising message. The serial number of theappliance that enables track to be kept of it may be printed or embossedon the rear face. It may include a serial number only, or else by aserial number followed by digits for verifying that it is authentic,e.g. if the serial number needs to be spoken by the user to an operatorwhen the appliance is first put into service.

The terminal can be sold in a sealed transparent pack that may alsocontain the batteries.

A label may be provided so that the user can write thereon the temporarycall number which is allocated when the terminal is put into service.

By way of example, the buttons may have the following functions:

Off O: when this button is depressed, power supply to the terminal isswitched off; no transmission or reception is possible.

Standby S: this position allows calls to be received. In this state, aprogram periodically checks and memorizes whether the power supply issufficient, turns on a voltage indicator and switches the terminal intoreceive mode, which may be the mode expected by the correspondingnetwork. Under such circumstances, a field measurement sequence isperformed automatically to seek the signal transmit and receivefrequencies of a beacon channel to inform the appropriate station of thepresence of the terminal, to perform signalling when a call is received,to select the conversation channel, and to provide a visible or anaudible indication when a call is being received. The terminal can bedesigned to return to off mode after a certain length of time haselapsed in order to save batteries.

Answer A: this position enables the user to take the line, if the userso desires, on receiving warning of an incoming call. Actuating thisbutton puts the vocoder module into operation.

Call C: this position enables a call to be made with automaticconnection to the server center via the radio network. Again the programperiodically checks that the power supply is sufficient and controlslighting of an indicator to specify that the appliance is powered and toswitch the terminal into call transmit mode. By way of example, when theterminal is used in a GSM system, fields are measured to seek a transmitfrequency, to seek a beacon channel for enabling the network to locatethe terminal, for signalling (call transmission), for selecting theconversation channel, for transmitting the terminal identity sequence(to enable the server center to initialize account debiting or to refusethe call in the event of loss, theft, or exhaustion of credit), puttingthe transmit module and the vocoder module into operation. At systemlevel, routing may take place automatically to a backup number for theserver center if the server is busy.

Given that power is taken from batteries, which are of limited lifetime,it can be advantageous to use a transmit module whose power isadjustable and to adjust its power as a function of its closeness to arelay point, as determined by field measurements.

The block diagram of the terminal may be as shown in FIG. 3. Itcomprises a management module 20 and a mobile network module 22 both ofwhich may be integrated circuits as currently available on the marketfor GSM terminals or for simplified modules. The module is connected toa receiver 24 and to a transmitter 26, each of which comprises anamplifier and both of which are connected to an antenna 28. The antennamay be printed directly on the card which carries the integratedcircuit. A vocoder 32 supplies the audio signal which is output to anearphone 34 and receives the audio signal for processing from amicrophone 36. It is connected via a switching circuit 38 to thetransmitter and to the receiver. The data required for operation isstored in a memory 40.

When it is desired to minimize cost (as is often the case), the terminaldoes not have means for transmitting and receiving data other than thedata mentioned above, given that such means would put constraints oninitializing the terminal on the first occasion it is put into service.

The management modules are connected to the standby button 14 a, thecall button 14 b, the answer button 14 c, and the off button 14 d. Themanagement module is also connected to a component 16 for giving warningof an incoming call, e.g. a ringer 42.

The system may be designed to reduce the risk of theft, or at least tomake it less profitable. Two types of theft are to be feared, theft ofan entire batch of telephones and snatch theft of a single telephone.

One measure consists in giving each terminal an identification numberprinted on the back that the purchaser must utter on making the firstcall. The number can be encoded by means of a secret key so that anumber given at random will not satisfy the code and a number taken fromanother telephone will be identified as having been allocated already.Another solution consists in informing the distributor under separatecover of a word that the purchaser needs to utter.

An individual stolen telephone can be invalidated on a complaint beingmade by the legitimate holder thereof, merely by setting its account tozero.

What is claimed is:
 1. For use in a digital radio telephony systemcomprising: a cellular telephony network having at least one callcenter; and a plurality of portable terminals each having memory meansfor storing terminal identity data, said call center including means foridentifying portable terminals that have been sold or manufactured fromthe identity data thereof, means for managing payments by debiting aninitial account allocated to each terminal, and means for managing androuting calls originating from said portable terminals, a portableterminal including a vocoder connected to transceiver means using adigitally modulated carrier for transmitting and receiving a speechsignal, a memory preprogrammed and protected again writing, the memorycontaining said identifier, a call button for calling only said callcenter having a number that is predefined and stored in the terminal,said call button causing the number of the single call center to betransmitted, and means for sending the identifier to the call center. 2.A terminal according to claim 1, wherein said call button has only off,standby, and answer mode positions, in addition to a call position.
 3. Amethod of digital radio telephony including the steps of: providing asystem having a fixed network having at least one call center and aplurality of portable terminals each being devoid of calling meansexcept means capable of calling only said call center; assigning apredetermined credit of telephone charging units to each of saidportable terminals prior to sale of said terminals; when a first call ismade from one said terminal to the call center, transmitting anidentifier to the single call center from the terminal and transmittinga temporary subscriber number from the call center to the terminalresponsive to said call, thereby enabling said terminal to be called viathe network; storing said subscriber number at the call center; and onsubsequent calls from said terminal to the call center, setting up therequested connection via the call center and debiting telephone chargingunits from the initially assigned charging units.
 4. A method accordingto claim 3, wherein, responsive to the first call, the temporarysubscriber number is given to the terminal by voice by voice synthesisand on each subsequent call, and on each subsequent call the holder ofthe portable terminal indicates the called number vocally, said numberbeing identified by speech recognition at the call center.
 5. A methodaccording to claim 4, including the step of informing the holder of theportable terminal of the balance remaining from the call center by voicesynthesis.
 6. A method according to claim 3, wherein on the first callthe call center records the temporary number; and when the credit hasbeen used up, the call center invalidates the terminal.
 7. A methodaccording to claim 6, characterized in that during manufacture or sale,an identifier stored in the terminal is recorded at the call center, andin that on each occasion a call is made, a check is performed on saididentifier.
 8. A method according to claim 6 wherein after creditexhaustion, calls from the terminal are rejected by the network.
 9. Amethod according to claim 8, characterized in that the possibilityremains of receiving calls from the network during a determined periodof time after the credit has been exhausted, after which time theterminal is invalidated and its subscriber number is released by thecall center.
 10. A method according to claim 6, wherein, in response tothe first call, the temporary subscriber number is given to the terminalby voice synthesis.
 11. A digital radio telephony system comprising: acellular telephony network having at least one call center; and aplurality of portable terminals each having memory means for storingterminal identity data and a call number for a single said call center,and each devoid of calling means except means for transmitting said callmember, said call center including means for identifying portableterminals that have been sold or manufactured from the identity datathereof, means for managing payments by debiting an initial accountallocated to each terminal, and means for managing and routing callsoriginating from said portable terminals.